1. Field of the Invention
The invention relates to a method for determining an impact point of a fired projectile relative to a target. More specifically, reference is made in this context to gunfired projectiles.
2. Discussion of the Background
When firing projectiles, it is of importance to ascertain the position where the projectile will come down or hit, for instance for comparing this position with a previously predicted point, the predicted hitting point (PHP). The firing direction of a subsequent projectile can then be adjusted, which procedure is known as In Action Calibration (IAC). Besides, it is often important to provide an indication of the distance by which the projectile misses the target, the so-called Miss Distance Indication (MDI).
It is customary to determine the impact point by means of a search radar system. Particularly in case of applications in a maritime environment, for instance at sea, the projectile position is measured at the moment that it hits the water and detonates. This causes a column or splash of water in an upward direction. On land, projectile detonation will cause a dust cloud. The splash or dust cloud can be registered by the search radar, thus enabling the impact point to be determined.
The drawback of such a method is that the splash is relatively poorly visible on radar displays. Since the target usually produces a very strong echo compared to the splash, the radar echo produced by the splash will sometimes even be eclipsed by the radar echo produced by the target. If the projectile impact occurs close to the target, the limitation of the radar resolution and the radar system's limited dynamic range exclude the possibility of distinguishing between target and splash and among the splashes. Besides, state-of-the-art search radar systems provided with TWT (Travelling Wave Tube) transmitters emit long pulses. When processing received echoes, this causes time side lobes which manifest themselves in a reduced range resolution. A second drawback of a search radar system is the comparatively low update rate of target and splash measurements. In addition, it is difficult, in case of a plurality of splashes caused by separate projectiles, to coordinate, per search radar revolution, the measurements pertaining to a single splash, which is partly due to the fact that not all splashes produce equally strong radar echoes.
However, naval ships are as a rule also provided with tracking radar systems, usually comprising transmitters for generating short pulses, particularly suitable for air target tracking. This ensures a good resolution. Moreover, tracking radars have a far higher update rate.